Exoplanetology: Exoplanets & Exomoons

The CO-Fuelled Time Machine: Tracing Birth Conditions and Terrestrial Planet Formation Outcomes in HD 163296 through Pebble Drift-induced CO Enhancements

By Keith Cowing

Status Report

astro-ph.EP

January 11, 2025

Filed under astro-ph.EP, CO snowline, dust grains, exoplanet, HD 163296, Interstellar, Markov Chain Monte Carlo, planet formation, Protoplanetary Disk, snowline, super-Earth, Terrestrial Planet

The CO-Fuelled Time Machine: Tracing Birth Conditions and Terrestrial Planet Formation Outcomes in HD 163296 through Pebble Drift-induced CO Enhancements — Schematic illustrating transport mechanisms of volatiles that produce the C/H enhancement seen within the CO snowline in HD 163296 as observed by Zhang et al. (2020). The process begins in the outer disc with dust growing to pebbles as the CO and water vapour freeze out onto the pebbles. As the grains grow, they decouple from the gas and drift inwards towards the CO snowline; within the snowline, the CO sublimates and enhances the C/H ratio of the gas and vapour present; the CO vapour is transported to the upper layers of the disc via diffusion. It also advects inwards, indicated by the grey arrows. Water ice remains on the pebbles and is transported further inward as the pebbles continue to drift toward the water snowline, which is around 1 AU in our model in this paper. Here, water sublimates and becomes readily available for planet formation in the region where terrestrial planets may be forming. Note that the illustrated emission line probe region is specific to CO rotational lines in this context. This schematic was inspired by Fig. 2 of Cuzzi & Zahnle (2004). — astro-ph.EP

The architecture and composition of planetary systems are thought to be strongly influenced by the transport and delivery of dust and volatiles via ices on pebbles during the planet formation phase in protoplanetary discs.

Understanding these transport mechanisms is crucial in building a comprehensive picture of planet formation, including material and chemical budget; constraining the birth properties of these discs is a key step in this process.

We present a novel method of retrieving such properties by studying the transport of icy pebbles in the context of an observed gas-phase CO enhancement within the CO snowline in the protoplanetary disc around HD 163296.

We combine Markov Chain Monte Carlo (MCMC) sampling with a fast model of radial drift to determine the birth gas mass and characteristic radius of the disc, and compare our results against observations and models in the literature; we find the birth-condition disc gas mass to be log₁₀(M_disc/M_⊙)=−0.64^+0.19−0.24 and the characteristic radius to be log₁₀(r_c/AU)=2.30^+0.45−0.46.

We additionally determine that dust grains must be `fragile’ (v_f=100 cms⁻¹) to retain enough dust to match current dust mass observations, with our lowest fragmentation velocity model providing a current-age dust mass of M_dust=662^+518−278M_⊕ based on the retrieved birth conditions.

Using our retrieved birth conditions, we extend our simulations to mass of material reaching the water snowline in the inner disc, where terrestrial and super-Earth planets may be forming, and speculate on the nature of these exoplanets.

Joe Williams, Sebastiaan Krijt

Comments: 15 pages, 12 figures, 2 tables; accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.05316 [astro-ph.EP] (or arXiv:2501.05316v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.05316
Focus to learn more
Submission history
From: Joe Williams
[v1] Thu, 9 Jan 2025 15:34:07 UTC (1,110 KB)
https://arxiv.org/abs/2501.05316
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter